Acidizing a hydrocarbon formation is the process of reacting an acid in the formation to enhance the flow of hydrocarbons to the wellbore. This can be through the dissolution of existing formation material or through the removal or bypass of blockage, often referred to as “damage to the well” which can be caused by natural or man-made conditions. Acidizing, or acid stimulation, opens up the channels around the wellbore, thereby improving the flow rate. When acid is injected into a formation, permeability is increased, thus enhancing the flow of hydrocarbons to the wellbore. This results in an increase or improvement in production from the formation.
Prior to introducing fluids into the formation, it is desirable to first determine fluid flow parameters by reservoir modeling techniques. Two key measured properties are porosity and permeability of the reservoir. The porosity of a material is the ratio of the aggregate volume of its void or pore spaces (i.e., pore volume) to its gross bulk volume and, in the case of an oil or gas reservoir, is a measure of the capacity within the reservoir rock which is available for storing oil or gas. The permeability of a material is a measure of the ability of the material to transmit fluids through its pore spaces and is inversely proportional to the flow resistance offered by the material. It is important that such fluid flow parameters be determined by reservoir modeling prior to commencement of treatment.
Porosity and permeability are determined by taking core samples from the reservoir site and carrying out well-defined measurement techniques on the samples. There are several techniques available for making such measurements. Effective radial modeling is difficult to perform due to constraints imposed by the amount of core material typically available. A true radial model would require very large blocks of reservoir material to effectively model flow patterns and stimulation properties of a given acid system. Since most reservoir coring operations generate 4″ diameter (or smaller) cylindrical cores, obtaining large blocks of intact reservoir is in most cases impossible. Therefore, an improved method of radial stimulation reservoir modeling is desired.